This invention relates to a fluid pump with a rotary impeller, and more particularly to a fluid pump with a bearing-free, seal-free electromagnetically-driven rotary impeller, levitated by a combination of axial and radial localized opposed repulsive magnetic and fluid forces or by repulsive axial and radial magnetic forces only.
Levitation of the impeller by such forces allows for high efficiency in converting power into useful work. Thus, a relatively small energy source can be used and the life of the energy source is correspondingly extended. Moreover, use of a levitated impeller driven by electromagnetic forces eliminates the need for driving mechanism bearings and seals, thereby avoiding the heat build-up and leakage attendant with other rotary pump inventions. Such considerations can be of critical importance for pumping of physiological fluids such as blood.
A large number of mechanisms for pumping fluids have been described in the art, including, for example, peristaltic pumps, moving diaphragm pumps, piston-type pumps, and centrifugal or rotary pumps. Generally, a rotary pump includes a pumping chamber with inlet and outlet ports and an impeller mounted within the pumping chamber for rotation about an axis. Frequently the impeller is mounted on a shaft that extends through one or more seals and a bearing apparatus to a rotational driving mechanism outside the pumping chamber. Rotary pumps employing shaft-mounted impellers with shaft seals are exemplified in the following U.S. patents: Dorman et al. U.S. Pat. No. 3,608,088; Rafferty et al. U.S. Pat. No. 3,647,324; Reich et al. U.S. Pat. No. 4,135,253; Clausen et al. U.S. Pat. No. 4,589,822; Moise U.S. Pat. No. 4,704,121; and Kletschka U.S. Pat. No. 4,844,707. Shaft seals are susceptible to wear and heat build-up, which can lead to leakage and, in the case of blood pumps, to thrombogenic (clot-forming) problems, denaturation of proteins, and embolic phenomena and the like.
Other pump inventions employ liquid or hydrostatic bearings to reduce heat build-up and/or to dissipate heat and to reduce frictional forces in rotation of the shaft and/or impeller. In these inventions liquid or gas is forced into narrow clearances between the shaft and various bearing assemblies or between the impeller and the impeller housing. The relatively thin fluid or gas films generated in these inventions are nevertheless subject to high shear forces and some incremental heat build-up. The following U.S. patents exemplify the use of such liquid or hydrostatic bearings: Prindle U.S. Pat. Nos. 845,816 and 888,654; Anderson U.S. Pat. No. 2,864,552; Baker et al. U.S. Pat. No. 3,122,101; and Kambe et al. U.S. Pat. No. 4,475,866.
Olsen et al. U.S. Pat. No. 4,688,998 discloses a fluid pump with an electromagnetically driven and levitated impeller. In Olsen et al., a sensor and a controller is provided to sense and control the amount of electromagnetic levitating force applied to the impeller. Only electromagnetic levitating forces are applied to the impeller. Unlike the present invention, in Olsen et al. no fluid forces are available for levitation and, moreover, the electromagnetic levitated forces are not applied to the impeller in separate and distinct axial and radial directions. Consequently, a sensor and controller is necessary to adjust levitation of the impeller, which is not necessary in the present invention. While Olsen et al. eliminates the impeller drive shaft, bearings and seals, electrical power is required not only to drive the impeller but also to maintain the impeller in a suspended state. Moreover, the invention requires cooperating electromagnetic sets, sensors, suspension circuits, and sensing circuits for continuously adjusting the position of the impeller in the pump housing.
In the fluid pump disclosed in the parent application, from which this application is a continuation-in-part, while all the input energy is directed to rotation of the impeller, a portion of the input energy from the peripheral region of the impeller (which includes locations downstream from the periphery of the impeller) is diverted for use in levitating the impeller. Thus, not all of the input energy is directed toward pumping fluid. It would therefore be a significant advancement in the art to provide a novel pump apparatus whereby the impeller is levitated and positioned in the pump fluid by auto-adjusting, permanent repulsive magnetic forces and whereby it is possible for more input energy to be directed to rotation of the impeller and pumping of the fluid. Such a novel pump apparatus is disclosed and claimed herein.